7.59. ioctl VIDIOC_SUBDEV_G_FMT, VIDIOC_SUBDEV_S_FMT¶
7.59.1. Name¶
VIDIOC_SUBDEV_G_FMT - VIDIOC_SUBDEV_S_FMT - Get or set the data format on a subdev pad
7.59.2. Synopsis¶
-
VIDIOC_SUBDEV_G_FMT
¶
int ioctl(int fd, VIDIOC_SUBDEV_G_FMT, struct v4l2_subdev_format *argp)
-
VIDIOC_SUBDEV_S_FMT
¶
int ioctl(int fd, VIDIOC_SUBDEV_S_FMT, struct v4l2_subdev_format *argp)
7.59.3. Arguments¶
fd
File descriptor returned by
open()
.argp
Pointer to struct
v4l2_subdev_format
.
7.59.4. Description¶
These ioctls are used to negotiate the frame format at specific subdev pads in the image pipeline.
To retrieve the current format applications set the pad
field of a
struct v4l2_subdev_format
to the desired
pad number as reported by the media API and the which
field to
V4L2_SUBDEV_FORMAT_ACTIVE
. When they call the
VIDIOC_SUBDEV_G_FMT
ioctl with a pointer to this structure the
driver fills the members of the format
field.
To change the current format applications set both the pad
and
which
fields and all members of the format
field. When they call
the VIDIOC_SUBDEV_S_FMT
ioctl with a pointer to this structure the
driver verifies the requested format, adjusts it based on the hardware
capabilities and configures the device. Upon return the struct
v4l2_subdev_format
contains the current
format as would be returned by a VIDIOC_SUBDEV_G_FMT
call.
Applications can query the device capabilities by setting the which
to V4L2_SUBDEV_FORMAT_TRY
. When set, ‘try’ formats are not applied
to the device by the driver, but are changed exactly as active formats
and stored in the sub-device file handle. Two applications querying the
same sub-device would thus not interact with each other.
For instance, to try a format at the output pad of a sub-device,
applications would first set the try format at the sub-device input with
the VIDIOC_SUBDEV_S_FMT
ioctl. They would then either retrieve the
default format at the output pad with the VIDIOC_SUBDEV_G_FMT
ioctl,
or set the desired output pad format with the VIDIOC_SUBDEV_S_FMT
ioctl and check the returned value.
Try formats do not depend on active formats, but can depend on the current links configuration or sub-device controls value. For instance, a low-pass noise filter might crop pixels at the frame boundaries, modifying its output frame size.
If the subdev device node has been registered in read-only mode, calls to
VIDIOC_SUBDEV_S_FMT
are only valid if the which
field is set to
V4L2_SUBDEV_FORMAT_TRY
, otherwise an error is returned and the errno
variable is set to -EPERM
.
Drivers must not return an error solely because the requested format doesn’t match the device capabilities. They must instead modify the format to match what the hardware can provide. The modified format should be as close as possible to the original request.
-
v4l2_subdev_format
¶
__u32 |
|
Pad number as reported by the media controller API. |
__u32 |
|
Format to modified, from enum v4l2_subdev_format_whence. |
struct |
|
Definition of an image format, see |
__u32 |
|
Reserved for future extensions. Applications and drivers must set the array to zero. |
V4L2_SUBDEV_FORMAT_TRY |
0 |
Try formats, used for querying device capabilities. |
V4L2_SUBDEV_FORMAT_ACTIVE |
1 |
Active formats, applied to the hardware. |
7.59.5. Return Value¶
On success 0 is returned, on error -1 and the errno
variable is set
appropriately. The generic error codes are described at the
Generic Error Codes chapter.
- EBUSY
The format can’t be changed because the pad is currently busy. This can be caused, for instance, by an active video stream on the pad. The ioctl must not be retried without performing another action to fix the problem first. Only returned by
VIDIOC_SUBDEV_S_FMT
- EINVAL
The struct
v4l2_subdev_format
pad
references a non-existing pad, or thewhich
field references a non-existing format.- EPERM
The
VIDIOC_SUBDEV_S_FMT
ioctl has been called on a read-only subdevice and thewhich
field is set toV4L2_SUBDEV_FORMAT_ACTIVE
.
On success 0 is returned, on error -1 and the errno
variable is set
appropriately. The generic error codes are described at the
Generic Error Codes chapter.